The invention concerns an indicating instrument which is intended for a motor vehicle and has an illuminable display with a light-emitting substance which can be activated between two electrodes.
In the case of such indicating instruments, for indication purposes it is generally necessary to provide display areas which, in simple configurations, visually present the current situation to the user merely by means of a correspondingly illuminable character. While in the past respectively separate filament lamps together with a corresponding shield were used for this purpose, nowadays increasing use is being made of light sources which, apart from a low overall height and high operational reliability, also particularly permit illumination over a surface area.
A corresponding display has been realized for example by a substance consisting of phosphorus being induced to produce light emission by means of the two electrodes. By appropriate shaping of the electrodes or of the phosphorus layer, this allows characters or symbols to be depicted without an additional shield, then appearing for example as a light area before a dark background. In a similar configuration, background illumination is also provided, so that the characters or symbols become visible due to their contrasting color before an illuminated background.
When such illuminating means have been used in practice, it has proven to be disadvantageous that the customary indicating instruments usually have not only those displays which represent simple switching states, such as for example on/off, but in addition also other forms of representation such as pointer instruments, illuminated strips and increasingly also liquid crystal displays (LCDs), which each require a type of illumination matched specifically to them. For example, liquid crystal displays require transmitted-light illumination, in which the light spectrum undergoing a change as it passes through has to be taken into consideration, while dials for pointer instruments require uniform illumination of the scaling and possibly also active illumination of their pointer vane in a contrasting color. Furthermore, it is increasingly desired from design considerations for the indicating instrument to have a dark surface, so that the display only becomes visible to the viewer by means of corresponding illumination and thereby permits information to be provided on an individual, need-related basis.
There have already been attempts to illuminate the different components simultaneously by means of the actively illuminating display, in order in this way to simplify the construction and obviate the need for additional light sources. In practice, it has proven disadvantageous in this respect that either the luminous intensity of the display was not adequate, or was so only in a certain color spectrum, for illuminating further displays, or else the possibilities for shaping the displays were greatly restricted, so that the area of application was considerably restricted. In addition, undesired light changes occur at the interfaces of neighboring displays, leading to an inferior visual appearance of the indicating instrument.